Circular saw devices typically involve a circular or disc blade having an axial perforation or hole in its center. The blade is mounted to the blade using a shaft extending through the center hole and rotation thereof is driven by holding members concentrically mounted on the shalt and frictionally engaging the side faces of the blade.
Due to the presence of the shaft and of the holding members, the depth of cut of circular saws tends to be limited to less than the radius of blade. Therefore, some have come up with circular saw configurations where an annular blade is eccentrically driven. Such a configuration is described in U.S. Pat. Nos. 4,352,241, 4,472,880 and 4,793,065.
Briefly, these documents describe saw configurations where an annular blade is positioned between opposed rollers contacting the lateral faces of the blade. A driving roller in engaging the inner edge of the annular blade and rotation thereof drives the rotation of the blade about a virtual rotation axis. While such configurations allow increasing the depth of cut beyond the center of the blade, additional torque on the blade is required as the blade cuts deeper in the material. As the surface of the blade engaged by the drive rollers of the saw described in the prior art is very limited, slippage in-between the drive and saw blade have become a problem, thereby functionally limiting the depth of the cut.
Other annular saw configuration have been reported, where an annular blade is driven by a roller frictionally engaging one lateral face of the blade. Again, these configurations of the prior art tend to be unsatisfactorily since they do not overcome torque-related issues.
It would thus be advantageous to be provided with an annular saw capable of cutting beyond the rotation axis or center of the annular blade while maintaining sufficient torque between the drive rollers and the blade to satisfactorily enable such cutting depth.